Field of the Invention
The present invention relates to an automatic transmission for a vehicle, and more particularly, to a planetary gear train of an automatic transmission for a vehicle which implements forward 9-speeds and increases an entire speed ratio by a minimum configuration to improve power transmission performance and fuel efficiency and secure linearity of step ratios between transmission stages.
Description of Related Art
Recently, increasing oil prices have caused vehicle manufacturers all over the world to rush into infinite competition. Particularly in the case of engines, manufacturers have been pursuing efforts to reduce the weight and improve fuel efficiency of vehicles by reducing engine size, etc.
As a result, research into reduction of weight and enhancement of fuel efficiency through downsizing has been conducted in the case of an engine and research for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages has been conducted in the case of an automatic transmission.
However, in the automatic transmission, as the number of speed stages increases, the number of internal components also increases, and as a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components may be important in order to increase a fuel efficiency enhancement effect through the multiple speed stages.
In this aspect, in recent years, 8 and 9-speed automated transmissions tend to be implemented and the research and development of a planetary gear train capable of implementing more transmission steps has also been actively conducted.
However, improvement effect of fuel efficiency is not so good in case of an 8-speed automated transmission, because an entire speed ratio is maintained in a level of 6.5˜7.5.
Therefore, development of at least a 9-speed high efficiency automatic transmission is required in that operation efficiency of an engine and drivability of a vehicle are deteriorated because linearity of step ratios between transmission stages can't be secured in case of enabling an entire speed ratio of an 8-speed automated transmission to be a level more than or equal to 9.0.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.